A quote from HeadRoom website:

"At the very high end of headphone audio you’ll find balanced headphones and headphone amplifiers. Normally headphones have three connections: one to each ear and a common ground wire. The drive signal goes to one side of the driver coil in each earpiece, and the return from the coils joins together in the common ground connection. In a balanced headphone both sides of the driver coil are driven and no common connection between channels exists. Balanced amplifiers generate a normal and an inverted audio signal. The inverted signal is like a mirror image of the normal drive signal; when the normal signal is going positive the inverted signal is going negative. HeadRoom currently offers the Desktop Balanced Amp, the Home Balanced Amp, and the Max Balanced Amp. This method of driving headphones effectively doubles slew rate and power output, and halves the output impedance of the amp as seen by the headphones. The result is a dramatic improvement in speed, clarity, and impact. The downside is a significant investment in custom cables and amplifier electronics.
We currently offer four balanced headphones: The Sennheiser HD650, Sennheiser HD595s, beyerdynamic DT880, and Grado RS1. The Sennheiser HD650, is our favorite high-end can; it’s very refined and luscious sounding; a slightly laid back sound is its only fault, but that characteristic also makes them great for long listening sessions without fatigue."

Now, what I don’t understand (I’m really dumb when it comes to electronics) is how is that superior to simply getting rid of common ground? And if there are advantages why the same principal never used to drive speakers?


Also,
New Benchmark DAC1 USB.
A quote from Benchmark’s website:
"High-Current Output Drivers
The DAC1 USB features new high-current output drivers that are capable of driving 300-Ohm loads without an increase in distortion. They are also well suited for driving long cables or high-capacitance loads."

Does it mean I can use DAC1 USB’s balanced outputs to drive 300-Ohm Sennheiser HD650/600/580 headphones?

Can I simply re-terminate a stock HD650 cable replacement for balanced operation?
And if yes, what’s the pinout?
Unfortunately, readily available balanced cables offered by HeadRoom come with male XLRs.

Thanks in advance.

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Resistance - Liberty - Death to the oppressor

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And if there are advantages why the same principal never used to drive speakers?

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Actually, speakers are sometimes driven like this as bridged amplifiers work in this way. The main reason is that you can obtain a greater power output from a given supply voltage.

I'm not sure that there are any audible advantages in balanced operation for speakers and headphones though.

Cheers

James.

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JRP Music - Audio Mastering and Restoration.
http://www.jrpmusic.net

Thanks James.
It was something I didn’t know.

I also have Sonic Impact T-Amp. Which is very cheap but very good.
I read somewhere that T-Amp cannot be bridged for mono operation as it is already bridged, but until now I didn’t understand what it means.

T-Amp is capable of providing up to about 5W of ‘Audiophile Quality’ power for 8-Ohm speakers.

Is there anything wrong with using T-Amp as a balanced headphone amplifier?

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Resistance - Liberty - Death to the oppressor

My personal opinions here:

You have to take the audiophile people with a bit of salt. Quite a few of the claims made are "pseudo-scientific" in those circles, built on half digested science or understanding of technology that is not quite applicable. Another thing is that the target is always moving, the latest fad is always totally superior to the next latest.

Well, on to balanced headphone amplifiers. The first thing to know is that you can make an amplifier in many different ways. Balanced or unbalanced, class A, AB or even H and so on are very relevant to the designer, but quite uninteresting to the buyer. Take me working as designer as an exampel, I can botch any circuit making a mess of it. Others can make good sounding designs from any topology.

The claim that you double slew rate is one example of that half-digested stuff. It is true, that if have one circuit and than bridge it (making a balanced one) you get the double slew rate. But there are thousand different ways to double the slew rate if you wish. Which slew rate to aim for and how to achieve it is a design engineer question as a very high slew rate can make for an unstable circuit (and so on). Design choices ...

The DAC1 does not have so-called balanced outputs. It does drive HD600 very well.

Gunnar

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Now, what I don’t understand (I’m really dumb when it comes to electronics) is how is that superior to simply getting rid of common ground? And if there are advantages why the same principal never used to drive speakers?

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It's all rather misleading, and has nothing whatever to do with a common ground (or lack of it).. and the same principle is used to drive speakers, particular in in-car systems using (ground free) bridged amp configurations because of the limited 12V power supply typically found in cars.

The main issue here revolves around this statement:
"This method of driving headphones effectively doubles slew rate and power output, and halves the output impedance of the amp as seen by the headphones".

This is true, but only in comparison with a system comprising the same amp in a single-sided configuration.

It is perfectly possible to build (unbalanced) headphone drivers with as high a slew rate, power output and low impedance. As many of the high end headphone amps demonstrate.

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Does it mean I can use DAC1 USB’s balanced outputs to drive 300-Ohm Sennheiser HD650/600/580 headphones?

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No, it means theye have included a decently engineered (unbalanced) headphone amp that is capable of driving 300ohm headphones (amongst others) very well via the usual TRS headphone socket.

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Can I simply re-terminate a stock HD650 cable replacement for balanced operation?

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You could, but there would be no point, and it wouldn't work with many outputs properly.

Hugh

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Technical Editor, Sound On Sound

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Is there anything wrong with using T-Amp as a balanced headphone amplifier?

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YES. It isn't designed to be used that way!

hugh

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Technical Editor, Sound On Sound

Isn’t designed to be used this way is hardly a good enough reason for not trying it.

Headphone amp in Benchmark DAC1 was designed to drive headphones with a minimum 30-Ohms impedance without increase in distortion but it didn’t stop you from trying Sony MDR7509 (24-Ohm).

Quote Hugh Robjohns:

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I also tried the headphone output, and this proved equally impressive. Driving a pair of low-impedance Sony MDR7509s, the DAC1 had masses of level and drive capability, producing crisp transients with no hint of compression or clipping, even when pushing out ridiculous sound pressure levels.

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Anyway, someone else asked the same question on diyaudio forum and the question was answered by a nice guy going by the name panomaniac:

Quote panomaniac:

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Class-D is a bad idea for headphones for several reasons.

1) More power than you really need. Headphones require very little power compared to normal speakers, so many of the problems of power amps are not much of a concern for headphones. As stated above, Class-A amps would seem a good choice here.

2) Tons of noise. Class-D amps are noisy, by headphone standards. If you plug headphones directly into a class-D amp, even a small one, you'll hear what I mean! This noise is not a problem with normal speakers as they are so much less sensitive than phones.

3) The output filter. Switching amps use an low-pass output filter the is usually designed to work with a 4~8 ohm load. Headphones are often 32 ohms or more, so the filter response will be wrong.

4) H-Bridge design. The small Tripath chips used in the Sonic, Charlize, Fenice 20, AMP6, AMP3, etc. are bridged. Thus the left and right grounds can not be tied together. You would have to rewire your headphones to dual mono.

For the same money, size and trouble, a good Class-A amp, solid state or tube, even opamp, should give you better sound.

Hope that helps.

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Thanks anyway.
You are still the best.

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Resistance - Liberty - Death to the oppressor

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Isn’t designed to be used this way is hardly a good enough reason for not trying it.

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You can't use an unbalanced headphone amp as a balanced driver. Something is missing...

And if you do try and bodge it to work as a balanced driver, there is a fair chance you'll end up blowing one or other output amp in the process.

It's your call, obviously, but there seems little point in asking for advice if you are simply going to ignore it, and immemsely frustrating to argue the toss from a position of no knowledge with those who do know what they are talking about.

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Headphone amp in Benchmark DAC1 was designed to drive headphones with a minimum 30-Ohms impedance without increase in distortion but it didn’t stop you from trying Sony MDR7509 (24-Ohm).

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Maybe that's because as a fully qualified electronics engineer I have an inkling of what the specifications mean and what the limitations are practical implications of such specifications are... Yes, a 24ohm load impedance will compromise the DAC headphone amp's performance at the edge of the envelope. But not in a dangerous manner and not such that it becomes a practical issue if used sensibly. There is a world of difference between using a load which is a little low on a well designed and protected amp, and trying to use the amp in a mode it can't ever support.

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Anyway, someone else asked the same question on diyaudio forum and the question was answered by a nice guy going by the name panomaniac:

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He was apparently answering a different question to the one you posed here originally (although had it been asked here would have had a similar answer). However, basically, he is saying Class A (unbalanced) outputs are the preferred solution for headphone amps ... which is what we've all been saying further up this thread!

I don't think we ever got onto the whole Class D amp issue, but he is right in his suggestions about that for this application too.

hugh

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Technical Editor, Sound On Sound

Hugh,
I didn’t ignore anyone’s advice. And I don’t try to prove anything here I just want you to know that I’m not an idiot you think I am.

Sonic impact T-Amp is a very small and very cheap power amplifier that is very popular with audiophiles. I thought you heard about it as it had some really sensational reviews.
It can be powered by AA batteries and from the back it looks like this:

T-Amp is already bridged which means balanced, right?
Just like car amps you’ve mentioned in this thread.

What I was thinking of doing was to simply snip the jack off the HD650 headphone cable (the cable is easily replaceable so it’s not a big deal) and connect wires to T-Amp’s spring clips. As long as I’d start with a volume knob at it’s minimum I don’t see how I could blow anything. I could try it at any moment but I didn’t because I do listen to your advice.

By the way, the question on diyaudio was about using T-Amp as a headphone amp.
From what I know now it would be impossible to use it as a single ended amp because it’s already balanced.

Have a nice weekend and thanks for your time.

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Resistance - Liberty - Death to the oppressor

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I just want you to know that I’m not an idiot you think I am.

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I don't think you're an idiot. It just seems that you aren't taking in what I and others have been saying. Apologies if that is not the case.

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T-Amp is already bridged which means balanced, right?
Just like car amps you’ve mentioned in this thread.

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No, not really. Bridging and balancing are technically very different things. For a start, balancing requires matched impedances, bridging doesn't. Your amp has bridged outputs, NOT balanced outputs.

Many in-car amplfiiers do use bridging, for the same reasons as the Sonic-T device -- to achieve higher output power levels from low voltage supplies.

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What I was thinking of doing was to simply snip the jack off the HD650 headphone cable (the cable is easily replaceable so it’s not a big deal) and connect wires to T-Amp’s spring clips. As long as I’d start with a volume knob at it’s minimum I don’t see how I could blow anything.

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Yes, you could do as you suggest. In fact, if you really want to hook up your headphones to the Sonic-T's speaker outputs you will have to rewire them this way because, as you say, the amps negative terminals aren't linked to a common ground as they are in most amps... and shorting them together would cause problems.

It is unlikely, I grant you, that rewiring your headphoens as you suggest will blow anythign up... but without understanding the specific output circuit design and protection arrangements it is impossible to know for sure.

The bottom line is that this is a pretty low cost device so it is very possible that protective circuitry was low on the list of design priorities.

Clearly, your headphones will present a much higher impedance load than the output devices are optimised for. That in itself shouldn't be a problem, but it could affect the operation of whatever output device protection circuitry might be in use, and potentially even more seriously, affect any output filtering that is involved -- potentially resulting in ultrasonic instability and the release of the all-important black smoke!

Given that rewiring your headphones and misusing the Sonic-T in this way is extrenmely unlikely to result in improved sonic performance (as others elsewhere have explained to you), it seems to me to be a pointless and destructive exercise.

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From what I know now it would be impossible to use it as a single ended amp because it’s already balanced.

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Here we are again. A Single Ended amp is a specific design of amplfier topology. What you are talking about, I presume, is using the Sonic-T it as a single channel amp by bridging its outputs -- which you can't do because each channel is already bridged internally, as you know.

And as I said earlier, bridging is not the same as balancing. each channel of your amp is bridged, not balanced.

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Have a nice weekend and thanks for your time.

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No problem, and enjoy yours too.

hugh

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Technical Editor, Sound On Sound